1. Technical Field
The present subject matter relates to a method for localising an on-board unit to an area around a radio beacon. The present subject matter also relates to a radio beacon for such a method.
2. Background Art
In modern road toll systems, vehicles are equipped with on-board units (OBUs), with the aid of which the vehicles are located and their road use can then be evaluated and/or billed. To this end, a plurality of radio beacons are distributed over the road network, each having a limited radio coverage area, in which they can communicate with the OBUs of passing vehicles via radio, wherein a successful radio communication locates the OBU to the radio coverage area. The communication of the OBU with the radio beacon can here be based on DSRC (dedicated short range communication), WAVE (wireless access for vehicular environment), RFID (radio-frequency identification) or similar technologies, and the OBUs may accordingly be of the active or passive (transponder) type.
When a road has a number of lanes and an assignment of a passing vehicle to a lane is necessary, each lane is generally assigned a dedicated radio beacon. The radio coverage area (the communication zone) of the respective radio beacon must be limited here to the lane as best as possible by adapting the transmission strength of the radio beacon to the reception sensitivity of the OBU (and vice versa) in order to avoid the addressing or the detection of vehicle OBUs in adjacent lanes (what is known as “cross-talk”). This problem is particularly significant with roads having individual lanes (single lanes), since an addressing of a vehicle in a lane such as a lane travelling in the opposite direction would disrupt the operation, or with multi-lane roads, in which case the lane assignment is important, for example in the case of HOV (high occupancy vehicle) lanes.
This problem is aggravated by the fact that increasingly greater sensitivities and transmission strengths on the part of the OBUs can be achieved due to the continued technical development of the transceiver or transponder modules, whether active or passive, used in the OBUs, for example passive ISO-18000-63 chips. In addition, it is increasingly required for the described toll systems to be extendable to a number of countries and for OBUs of various national operators to be usable interoperably in these systems. A large number of models of OBUs with a wide range of different reception sensitivities and transmission strengths can thus be used in a road network, which leads to increased cross-talk.
WO 2010/105349 A1 shows a communication system between an antenna and an OBU. The OBU sends a message indicating its OBU type to the antenna, whereupon the antenna can localise the OBU by means of the received OBU type and a measured received signal strength of the message.
EP 2363826 A2 shows the localisation of RFID Tags from which an identifier is read out too. The localisation of the RFID Tags is carried out by reading out a parameter corresponding to the identifier.
U.S. Pat. No. 7,385,525 B2 shows a method for localising a vehicle on a lane by means of handshakes between an antenna and an OBU of the vehicle.